Historically the meter readings of the consumption of utility resources such as water, gas, or electricity has been accomplished manually by human meter readers at the customers' premises. The relatively recent advances in this area include collection of data by telephone lines, radio transmission, walk-by, or drive-by reading systems using radio communications between the meters and the meter reading devices. Although some of these methods require close physical proximity to the meters, they have become more desirable than the manual reading and recording of the consumption levels. Over the last few years, there has been a concerted effort to automate meter reading by installing fixed networks that allow data to flow from the meter to a host computer system without human intervention. These systems are referred to in the art as Automated Meter Reading (AMR) systems.
An AMR system consists of three basic components: an Encoder-Receiver-Transmitter (ERT); a Data Collection Unit (DCU); and an AMR computing system. The ERT is a meter interface device attached to the meter, which either periodically transmits utility consumption data (“bubble-up” ERTs), or receives a “wake up” polling signal or a request for their meter information from the DCU (e.g., a fixed transceiver unit, a transceiver mounted in a passing vehicle, a handheld unit, etc.) The ERT, either periodically or in response to a wake-up signal, broadcasts the meter number, the meter reading, and other information to the DCU. The DCU collects the information from the ERTs for subsequent retransmission to the AMR computing system. The AMR computing system receives the newly collected meter readings and updates the appropriate accounts of the billing system.
The ERTs typically communicate with the DCU via wireless spread-spectrum modulation protocols, such as direct-sequence spread-spectrum (DSSS) and frequency-hopping spread-spectrum (FHSS). DSSS combines a data signal at the ERT with a higher data-rate bit sequence, sometimes called a “chipping code” or “processing gain.” A high processing gain increases the signal's resistance to interference. FHSS, on the other hand, operates by taking the data signal and modulating it with a carrier signal that hops from frequency to frequency as a function of time over a wide band of frequencies. With FHSS, the carrier frequency changes periodically, and therefore, potentially reduces interference since an interfering signal from a narrowband system will only affect the spread-spectrum signal if both are transmitting at the same frequency and at the same time.
However, in the FHSS systems described above, interference from various sources, such as geographical obstructions, unlicensed radios, portable phones, and the like, decrease the probability that transmissions will be received.